1. Field of the Invention
This invention relates to a structure for a multi-layered dielectric layer and a manufacturing method thereof, and more particularly, to a structure and a manufacturing method of multi-layered dielectric layer in which an opening with a tapered profile is formed thereon.
2. Description of Related Art
In a manufacturing process of metallization for integrated circuits, a conductive area is provided for electrical conduction, over which a plurality of conductive layers are formed for a metallization process. An opening formed between the first conductive layer and the conductive area is a contact hole. The other openings between the first conductive layer and the other conductive layers are so-called via.
A conventional process of metallization includes, at first, providing a substrate, in which possesses a conductive area. The conductive area can be a source/drain region in the substrate or a metal line. Then a dielectric layer is deposited over the conductive area. After that, a process of planarization is performed. Then the dielectric layer is etched with a photoresist mask to define an opening which is a contact hole or a via. Finally, a metal layer is deposited over the conductive area to complete a mounted structure between the metal layer and the conductive area.
Regarding the conventional process above-described, there are some problems encountered for requirements of more intensive integration of integrated circuits. Referring to FIGS. 1a to 1d, showing cross-sectional views of several conventional methods for metallization.
Referring to FIG. 1a, shown the first conventional method for metallization. A dielectric layer 102 is formed over a conductive area 100 above a substrate 1. An opening, for example, an opening 10 is formed by a procedure of performing exposure, developing, and etching. The opening 10 possesses a nearly rectangular profile because of using an anisotropic etching. The more the integration intensity of integrated circuits, the closer the width between every two adjacent openings. When the width between the openings is decreased, the aspect ratio of the opening is correspondingly increased. It causes a bad performance of step coverage in the following process.
A structure of an overhang, for example an overhang 101a and an overhang 101b, is formed while a metal layer 104 is being deposited over the conductive area 100.
If the metal layer 104 is continuously deposited, the adjacent overhangs in the same opening, for example, the overhangs 101a and 101b in the opening 10 is connected each other, and then a void 101c is formed between the overhangs 101a and 101b. The void 101c is uncovered while performing a planarization procedure, and then contamination materials such as polymer are formed over the conductive area 100 are dropped into the void 101c. It causes some problems happened in the conduction in devices of the conductive area 100. Moreover, the overhangs formed in the openings cause the step coverage of the metal layer 104 worse, which makes the quality of the transistors in the conductive area 100 be worse.
Regarding problems caused by the rectangular structure formed by an anisotropic etching of a dry etching method, a second conventional method is provided for improving these problems. Referring to FIG. 1b, a dielectric layer 112 is formed over a conductive area 110 above a substrate 1, and then the conductive area 110 is performed exposure, developed, and etched with a photoresist layer 116. The etching procedure is, at first, using a wet etching, and then using a dry etching. Upper portions of the openings formed in the dielectric layer 112 above the conductive area 110 are larger in diameter than lower portions of the openings, for example, a upper portion 20a of the opening 20 is larger in diameter than a lower portion 20b of the opening 20. It will improve the problems caused by the overhangs formed in the openings in the following procedure.
The second conventional improving method causes some problems. One of these problems is that the lateral etching will consume higher percentage of planner surface budget. The consume in planner surface budget will reduce the photolithography overlayer process window during interconnect lithography process steps.
Moreover, when the integration intensity of integrated circuits increases, the openings of the dielectric layer 112 become closer. The oblique gaps formed by way of the lateral etching of the wet etching procedure can be easily connected with the adjacent opening. For example, the gap 113 in the opening 20 and the gap 114 in the opening 30 can be easily connected because that the width 112 between the gap 113 and the gap 114 is smaller than the prior art shown in FIG. 1a. Such phenomena will cause the photoresist lifting at the dense contact area due to wet etching reducing adhesion area between photoresist and dielectric.
A third conventional method is provided with forming polymers on sidewalls of the dielectric layer in the openings by adjusting etching recipe. Referring to FIG. 1c, at first, a conductive area 120 is formed over a substrate 1. Then a dielectric layer 122 is formed over the conductive area 120. By performing a procedure of exposure, developing, and etching with a photoresist layer (not shown), openings desired are formed in the dielectric layer 122. Polymers are then formed on sidewalls of the dielectric layer 122 in all openings by adjusting the etching recipe. For example, polymers 108 are formed in the sidewalls of the dielectric layer 122 in the opening 40 as shown in FIG. 1c. The polymers 108 may cause the contact metallization reliablility failure. The rate of the etching in upper portions of the opening is faster than the rate of the etching in lower portions of the opening. Therefore, an opening with oblique sidewalls can be easily formed. However, defects of the third conventional method are found that it is difficult to eliminate the polymers and the angle of the oblique sidewalls is also difficult to be controlled.
A forth conventional method is introduced by forming spacers on sidewalls of openings in a dielectric layer. Referring to FIG. 1d, well-proportioned conformal spacers, for example, spacers 134 are formed on sidewalls in an opening 50 above the dielectric layer 130. The spacers 134 can be consisted of dielectric materials, which are difficultly etched away. In the following process, the opening 50 with an oblique angle is formed owing to the protection of the spacers 134. However, defects of the forth conventional method can be found that the spacers 134 can not be uniformly formed onto the sidewalls of the openings formed above the dielectric layer 130. It causes an overhang structure formed on an upper portion of the sidewalls in the openings. Moreover, there are some defects such as poor capability of step cover, limitation of a ratio of height and width, a higher cost and reducing the diameter of the contact hole.